COVID-19 is here to stay, say experts, who believe emerging variants coupled with vaccine hesitancy is likely to make it impossible to achieve herd immunity in the U.S.

According to The New York Times, more than half of U.S. adults have had at least one dose of COVID-19 vaccines, but daily vaccination rates are falling. Scientists and public health experts now believe that reaching the threshold of immunity to stave off the virus is unattainable in the foreseeable future, and maybe forever.

What they predict is that COVID-19 will will remain for many years to come, causing hospitalizations and deaths, but to a much lesser degree than experienced so far.

"The virus is unlikely to go away," said Rustom Anti, Ph.D., a professor of biology and a faculty member at the Emory Vaccine Center at Emory University in Atlanta. "But we want to do all we can to check that it’s likely to become a mild infection."

Experts say that with the current mutations of SARS-CoV-2, the virus that causes COVID-19, the herd immunity threshold is 80%, according to the Times. Surveys show that 30% of Americans are hesitant to get vaccinated which pushes back the goal of achieving herd immunity even further.

Epidemiologists say COVID-19 will become an endemic disease, much like the seasonal flu. "I think if you speak with most epidemiologists and most public health workers, they would say that the disease will become endemic, at least in the short term and most likely in the long term," Dr. David Heyman, a professor of infectious disease epidemiology at the London School of Hygiene and Tropical Medicine, told CNBC.

According to The Washington Post, other experts agree that even with vaccines, there’s a good chance the virus will become endemic, meaning it probably will never go away. They noted that during these uncertain times, the "persistence of the novel virus is one of the few things we can count on about the future." According to the Post, the coronavirus will remain for decades to come, but like other endemic diseases, illnesses that are too stubborn to be stamped out, its severity most likely will decrease.

According to Nature, there are other reasons why herd immunity is unlikely. Experts point out that the vaccines that prevent severe illness from COVID-19 may not prevent transmission of the disease.

"Herd immunity is only relevant if we have a transmission-blocking vaccine. If we don’t, the only way to get herd immunity is to give everyone the vaccine," said Dr. Shweta Bansai, an associate professor in the Department of Biology at Georgetown University.

Another reason is that vaccine rollout has been uneven. While some areas have seen high rates of vaccinations, in rural areas the rates have been lower.

"If the coverage is 95% in the United states as a whole, but 70% in a small town, the virus doesn’t care," Dr. Marc Lipsitch, professor of epidemiology at the Harvard T.H. Chan School of Public Health and the director of the Center for Communicable Diseases, told the Times. "It will make its way around the small town."

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